Pulse arc welding control method and pulse arc welding device

ABSTRACT

A pulse arc welding device is controlled so as to weld an object by removing, from a welding wire, a molten droplet produced by melting the welding wire by applying a welding voltage between the welding wire and the object and allowing a welding current to flow through the welding wire such that the welding current alternately repeats, at pulse frequency, a peak current period in which the welding current is a peak current and a base current period in which the welding current is a base current smaller than the peak current. A removal time point at which the molten droplet is removed from the welding wire is determined. In a case where the removal time point is not in the base current period, a pulse waveform parameter which is at least one of the peak current and the peak current period is adjusted, and the pulse frequency based on a predetermined relationship between the pulse frequency and the pulse waveform parameter is adjusted so as to cause the removal time point to be in the base current period. This method allows a stable pulse arc welding.

TECHNICAL FIELD

The present invention relates to a pulse arc welding control method anda pulse arc welding device for performing a pulse arc welding whilefeeding a welding wire which is a consumable electrode.

BACKGROUND ART

In a conventional pulse arc welding machine, it is common to build adatabase of welding conditions suitable for each material, such as mildsteel and stainless steel, with the welding wire recommended by eachwelding machine manufacturer individually. For example, in a case of apulse waveform, parameters, such as peak current, base current, pulsefrequency, are adjusted while each operator of the welding machinemanufacturers checks construction and builds databases individually.

However, users using welding machines do not necessarily use the weldingwire recommended by the welding machine manufacturer. With respect tothe welding wires recommended by the welding machine manufacturer, amolten droplet transfer status is different from each other whenmaterial properties, such as viscosity and surface tension, of thewelding wires actually used by the user are different from each other.When the molten droplet transfer status is greatly different, thedroplet transfer status is not a droplet removal transfer due to thebase current period, such as one drop per one pulse (one time of dropletremoval per one pulse occurs) which is the fundamental droplet transferstatus of pulse arc welding, the droplet transfer status becomesunstable, e.g. one pulse n drop (multiple droplet removal occurs per onepulse) or one drop per number n of pulses (one time occurrence ofdroplet removal per multiple pulses).

Accordingly, since there is no regularity at the time point when themolten droplet of the droplet transfer is removed, an optimal databaseis required for each welding wire in order to perform stable welding.

Therefore, a pulse arc welding method is known in which the peak currentperiod continues until the molten droplet of the droplet transfer isremoved, and the droplet removal is surely caused one time per oneperiod of the pulse (See, for example, PTL 1).

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laid-Open Publication No. 60-180669

SUMMARY

A pulse arc welding control method uses a pulse arc welding device thatwelds an object by generating an arc between a welding wire and theobject. The pulse arc welding device is controlled so as to weld theobject by removing, from the welding wire, a molten droplet produced bymelting the welding wire by applying a welding voltage between thewelding wire and the object and allowing a welding current to flowthrough the welding wire such that the welding current alternatelyrepeats, at pulse frequency, a peak current period in which the weldingcurrent is a peak current and a base current period in which the weldingcurrent is a base current smaller than the peak current. A removal timepoint at which the molten droplet is removed from the welding wire isdetermined. In a case where the removal time point is not in the basecurrent period, a pulse waveform parameter which is at least one of thepeak current and the peak current period is adjusted, and the pulsefrequency based on a predetermined relationship between the pulsefrequency and the pulse waveform parameter is adjusted so as to causethe removal time point to be in the base current period.

This pulse arc welding control method allows the pulse arc weldingdevice to stably perform pulse welding, and provides a bead having apreferable shape.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an arc welding device according toExemplary Embodiment 1.

FIG. 2 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the pulse arc welding device according to Embodiment1.

FIG. 3 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of a comparative example of a pulse arc welding device.

FIG. 4 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the comparative example of the pulse arc weldingdevice.

FIG. 5 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the pulse arc welding device according to Embodiment1.

FIG. 6 illustrates a relationship between the pulse frequency and thepeak current of the pulse arc welding device according to Embodiment 1.

FIG. 7 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the pulse arc welding device in accordance withEmbodiment 1.

FIG. 8 illustrates a relationship between the pulse frequency and thepeak current period of the pulse arc welding device according toEmbodiment 1.

FIG. 9 illustrates a welding current of a comparative example of a pulsearc welding.

FIG. 10 is a schematic diagram of a pulse arc welding device accordingto Exemplary Embodiment 2.

FIG. 11 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the pulse arc welding device according to Embodiment2.

FIG. 12 illustrates a welding current, a welding voltage, and a state ofdroplet transfer of the pulse arc welding device according to Embodiment2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Exemplary Embodiment 1

FIG. 1 is a schematic diagram of pulse arc welding device 1001 accordingto Exemplary embodiment 1. Pulse arc welding device 1001 includeswelding power supply device 31 and robot 22 (manipulator).

Welding power supply device 31 includes primary rectifier 2 forrectifying an output of input power supply 1, switching element 3 thatcontrols a welding output by controlling an output of primary rectifier2, transformer 4 for insulating and converting the output from switchingelement 3 and outputting from secondary side output, secondary rectifier5 for rectifying an output from the secondary side output of transformer4, and reactor 6 (DCL) connected in series to secondary rectifier 5.Welding power supply device 31 further includes output controller 7 fordriving switching element 3, welding voltage detector 8, and weldingcurrent detector 9. Welding power supply device 31 further includesshort-circuit/arc detector 10, short-circuit controller 11, and arccontroller 12. Welding voltage detector 8 detects welding voltage Vbetween object 29 and welding wire 24. Welding current detector 9detects welding current I flowing through welding wire 24. Short-circuitcontroller 11 and arc controller 12 control output controller 7. Weldingpower supply device 31 further includes feeding speed controller 19 thatcontrols the feeding speed at which welding wire 24 is fed in accordancewith welding conditions, output terminal 30 a, and output terminal 30 b.

Arc controller 12 includes pulse waveform setting unit 14, pulsewaveform controller 15, and droplet-removal detector 13. Pulse waveformcontroller 15 includes peak current corrector 16, peak current periodcorrector 17, and pulse frequency corrector 18.

Robot controller 20 that controls an operation of robot 22 includeswelding condition setting unit 21 for setting welding conditions. Robotcontroller 20 is connected to welding power supply device 31 so as to becapable of communicating with each other. Torch 26 is attached to robot22. Torch 26 holds chip 27 holding welding wire 24.

Feeding speed controller 19 of welding power supply device 31 determinesa feeding speed corresponding to the setting current of welding currentI set in welding condition setting unit 21 provided in robot controller20, and outputs a signal indicating the feeding speed. In response tothe signal from feeding speed controller 19, pulse waveform setting unit14 of arc controller 12 outputs a pulse waveform parameter, such as peakcurrent IP and base current IB, according to the wire feeding speedindicated by the received signal. Pulse waveform controller 15 controlsa pulse waveform of the welding current based on the value of each pulsewaveform parameter. In addition, based on a signal from feeding speedcontroller 19, wire feeder 25 with a feed roller feeds welding wire 24.

Welding condition setting unit 21 of robot controller 20 connected towelding power supply device 31 sets, e.g. a welding current and awelding voltage. Output terminal 30 a of welding power supply device 31is electrically connected to chip 27 holding welding wire 24, andsupplies power to welding wire 24 via chip 27. Output terminal 30 b iselectrically connected to object 29 and supplies power to object 29. Arc28 is generated between a tip end of welding wire 24 and object 29. Wirefeeder 25 feeds welding wire 24 from welding wire storage 23 storingwelding wire 24 to chip 27 of torch 26.

Constituent portions of pulse arc welding device 1001 illustrated inFIG. 1 may be configured separately or may be configured by combiningplural constituent portions.

FIGS. 2 to 7 illustrates welding current I, welding voltage V, and astate of droplet transfer around welding wire 24 and object 29. Pulsearc welding device 1001 alternately repeats peak current period IPT inwhich welding current I is peak current IP and base current period IBTin which welding current I is base current IB smaller than peak currentIP, and generates an arc between welding wire 24 and object 29 toperform a pulse welding. Pulse arc welding device 1001 adjusts a pulsewaveform parameter that determines a waveform of welding current I whilemonitoring removal time point td at which molten droplet 24 d isremoved.

Welding current I has a pulse waveform which alternately repeats peakcurrent IP and base current IB smaller than the peak currentperiodically with pulse period PT. The pulse waveform illustrated inFIG. 2 is a basic pulse waveform providing a stable droplet transfer(removal) repeating in a period in which welding is steadily performed.Pulse period PT includes pulse rising period IPRT, peak current periodIPT, pulse falling period IPFT, and base current period IBT. In pulserising period IPRT, welding current I transits from base current IB topeak current IP. In peak current period IPT, welding current I is peakcurrent IP. In pulse falling period IPFT, welding current I transitsfrom peak current IP to base current IB. In base current period IBT,welding current I is base current IB. Arc length L28 of arc 28 isstabilized by pulse frequency PHz which is a reciprocal of pulse periodPT, and the droplet transfer is performed.

The pulse waveform parameters adjusted so as to realize so-called onedrop per one pulse, in which droplet 24 d is dropped onto object 29 onlyone time in one pulse period PT are different from each other accordingto welding conditions, such as object 29 and welding wire 24 to be used.Therefore, in order to realize the one drop per one pulse, weldingconditions, such as recommended welding wire and shielding gas, can bepreviously determined by confirming construction of experiments.

Molten droplet 24 d produced by melting welding wire 24 in pulse risingperiod IPRT starts growing (state Sa). Then, molten droplet 24 d growsto have an optimal size during peak current period IPT (state Sb). Next,during pulse falling period IPFT, constriction 24 p having a locallysmall diameter is produced (state Sc). Constriction 24 p exhibits astate of immediately before molten droplet 24 d is removed from the tipend of welding wire 24. After that, molten droplet 24 d is removed fromwelding wire 24 at removal time point td during base current period IBT(state Sd). After that, molten droplet 24 d produced by melting weldingwire 24 in pulse rising period IPRT starts growing, and molten droplet24 d is grown until molten droplet 24 d has a size enough to be removedfrom welding wire 24 in peak current period IPT (state Sf). Next, duringpulse falling period IPFT, constriction 24 p having a locally smalldiameter is produced at the tip of welding wire 24, is produced.Constriction 24 p exhibits a state of immediately before molten droplet24 d is removed. After that, molten droplet 24 d is removed from weldingwire 24 at removal time point td during base current period IBT (stateSg). The pulse waveform of welding current I illustrated in FIG. 2 is anoptimal waveform performing a basic molten droplet transfer in which onemolten droplet 24 d is removed from welding wire 24 only once in pulseperiod PT from pulse rising period IPRT to next pulse rising periodIPRT.

The transfer (removal) of molten droplet 24 d is repeated at pulsefrequency PHz which is the reciprocal of pulse period PT provides astable welding state and a bead having a preferable outer appearancewith less spatter.

FIGS. 3 and 4 illustrate welding current I, welding voltage V, and thestate of welding transfer in the state of the comparative example inwhich molten droplet 24 d is not stably removed.

In the pulse waveform of welding current I illustrated in FIG. 3, ascompared with the pulse waveform illustrated in FIG. 2 realizing a basicdroplet removal state where molten droplet 24 d is removed in basecurrent period IBT, welding wire 24 is excessively melted so that moltendroplet 24 d is unstably removed from welding wire 24. In the pulsewaveform illustrated in FIG. 3, molten droplet 24 d starts growing inpulse rising period IPRT (state Sa), and molten droplet 24 d is grownuntil molten droplet 24 d has the optimal size in peak current periodIPT (state Sb, Sc1). After that, molten droplet 24 d is removed fromwelding wire 24 at the tip of the welding wire at removal time point tdduring pulse falling period IPFT (state Sd1). The waveform of weldingcurrent I illustrated in FIG. 3 is a pulse waveform of a non-optimal,unstable molten droplet transfer (droplet removal) which is a statewhere molten droplet 24 d cannot be removed from welding wire 24 (stateSd) during base current period IBT after pulse falling period IPFT. Inother words, in welding current I illustrated in FIG. 3, removal timepoint td at which molten droplet 24 d is removed in pulse falling periodIPFT transferring from peak current period IPT to base current periodIBT is before base current period IBT, that is, is earlier than basecurrent period IBT.

As this molten droplet transfer (droplet removal) state is repeated atpulse frequency PHz, removal time point td at which molten droplet 24 dis removed may fluctuate, resulting in an unstable welding state.

The unstable molten droplet transfer (droplet removal) state illustratedin FIG. 3 is often produced in a state where the viscosity or surfacetension of the molten welding wire is lower than recommended weldingwire 24. In this case, the actually used welding wire 24 is melted or acase the ratio of the Ar gas of the shielding gas increases, withrespect to recommended welding wire 24.

In the pulse waveform of welding current I illustrated in FIG. 4, themolten droplet transfer is unstable as compared with the pulse waveformillustrated in FIG. 2 which realizes the fundamental droplet removalstate where molten droplet 24 d is removed in base current period IBT.In this case, molten droplet 24 d is not removed even when transferringfrom peak current period IPT1 in pulse period PT1 to base current periodIBT1. In pulse rising period IPRT1 in pulse period PT1, molten droplet24 d starts to grow (state Sa), and molten droplet 24 d is grown untilmolten droplet 24 d has the optimal size in peak current period IPT1(state Sb). Subsequently, in pulse falling period IPFT1 in pulse periodPT1, constriction 24 p which is a state immediately before moltendroplet 24 d is removed from the tip of welding wire 24 is not produced(state Sc2), and molten droplet 24 d cannot be removed from welding wire24 even in base current period IBT1 (state Sd2). Molten droplet 24 d isenlarged (state Se2) in peak current period IPT2 at removal time pointtd in pulse period PT2 next to pulse period PT1 and removed by gravity(state Sf2). The state of molten droplet transfer illustrated in FIG. 4is the most unstable. In welding current I illustrated in FIG. 4, moltendroplet 24 d is not removed even in a case of transferring from peakcurrent period IPT1 of a certain pulse period PT1 to base current periodIBT1, and molten droplet 24 d is finally removed at removal time pointtd during peak current period IPT2 of pulse period PT2 next to the pulseperiod PT1, that is, the time point at which molten droplet 24 d isremoved is late, and a state of one drop per n pulses is exhibited.

By repeating this molten droplet transfer (droplet removal) state atpulse frequency PHz, removal time point td at which molten droplet 24 dis removed largely fluctuates, resulting in an unstable welding state.

Such a molten droplet transfer (droplet removal) state often becomes anunstable state when welding wire 24 actually used has higher viscosityand surface tension of than the recommended material characteristics andwelding conditions of welding wire 24 or when the Ar gas ratio of theshielding gas is low.

In order to eliminate the unstable molten droplet transfer (dropletremoval) state due to the differences of welding wire 24 and theshielding gas as described above, in pulse arc welding device 1001according to Embodiment 1, removal time point td of molten droplettransfer (droplet removal) after the next period is adjusted by one orpulse waveform parameters so as to optimize removal time point td atwhich molten droplet 24 d is removed. Specifically, the state of moltendroplet transfer is monitored so as to be a state of one drop per onepulse which is an optimal state where molten droplet 24 d is removed(state Sd) in base current period IBT during pulse period PT. Accordingto removal time point td at which molten droplet 24 d in the moltendroplet transfer state is removed, the one or more parameters of adjustremoval time point td of molten droplet transfer (removal of moltendroplet 24 d) after the next period.

An example of adjustment of pulse waveform parameters in pulse arcwelding device 1001 according tp Embodiment 1 will be described below.

FIG. 5 illustrates welding current I, welding voltage V, and the stateof molten droplet transfer of pulse arc welding device 1001. In FIG. 5,removal time point td at which molten droplet 24 d is removed in themolten droplet transfer is adjusted by adjusting peak current IP.Specifically, in welding current I illustrated in FIG. 5, with respectto the molten droplet transfer state illustrated in FIG. 3 where moltendroplet 24 d is removed from the tip of welding wire 24 in pulse fallingperiod IPFT before base current period IBT (state Sc), the electricenergy applied to welding wire 24 is made appropriate by decreasing peakcurrent IP from peak current IP illustrated in FIG. 3 to decrease thearea of one peak of the pulse waveform of welding current I in one pulseperiod PT.

In welding current I illustrated in FIG. 5, since the area of the onepeak of the pulse waveform is decreased, in order to secure anappropriate melting speed of welding wire 24, the pulse waveformparameters (peak current IP and pulse frequency PHz) are adjusted sothat welding current I becomes a setting current that is an appropriateaverage value by decreasing peak current IP and shortening pulse periodPT, i.e., increasing pulse frequency PHz. This operation provides adroplet removal timing in an optimal state where molten droplet 24 d isremoved in base current period IBT while stabilizing arc length L28.

In the method described above for adjusting removal time point td atwhich molten droplet 24 d is removed in the molten droplet transfer byadjusting peak current IP, conversely, in the molten droplet transfer(removal) state illustrated in FIG. 4, the value of peak current IP ismade larger than peak current IP illustrated in FIG. 4 to increase thearea per one pulse period PT of the pulse waveform, and the electricenergy applied to welding wire 24 is made appropriate with respect tothe most unstable molten droplet transfer (removal) state (State Sf2) inwhich the molten droplet 24 d is enlarged and is removed by gravity inpeak current period IPT2 of pulse period PT2 next to pulse period PT1,not during base current period IBT1 of pulse period PT1.

In welding current I described above, since the pulse area is madelarge, in order to secure an appropriate melting speed of welding wire24, peak current IP is made large and pulse period PT is lengthened tolower pulse frequency PHz, thereby adjusting the pulse waveformparameter (peak current IP). This operation provides a droplet removaltiming in an optimal state where molten droplet 24 d is removed in basecurrent period IBT while stabilizing arc length L28.

An example of specific adjustment of peak current IP and pulse frequencyPHz in pulse arc welding device 1001 will be described below. FIG. 6illustrates a predetermined relationship between peak current IP andpulse frequency PHz, which is a pulse waveform parameter for optimallyadjusting the molten droplet transfer (droplet removal) state whilestabilizing arc length L28.

FIG. 6 illustrates the predetermined relationship between peak currentIP and pulse frequency PHz in a case where the diameter of welding wire24 is ϕ1.2 and the setting current of welding current I is 200 A inpulse MAG welding in which welding wire 24 is a mild steel, thereference value of peak current IP is 460 A, and the reference value ofpulse frequency PHz is 210 Hz.

Adjustment of pulse waveform parameters based on the relationshipillustrated in FIG. 6 of pulse arc welding device 1001 will be describedbelow in the case that welding wire 24 or shielding gas having differentconditions from the recommended conditions is used.

As illustrated in FIG. 3, in a case where molten droplet 24 d is removedbefore base current period IBT and the droplet removal timing is tooearly, it is determined that the melting speed of welding wire 24 is toohigh. On the other hand, in order to set the optimum pulse waveform areaas the melting speed of welding wire 24 based on the predeterminedrelationship between pulse frequency PHz and peak current IP illustratedin FIG. 6, in a case where peak current IP is made smaller thanreference value 460 A described above as 440 A, stable arc length L28can be secured by increasing pulse frequency PHz from reference value210 Hz to 215 Hz.

In contrast, as illustrated in FIG. 4, in a case where molten droplet 24d is not removed during base current period IBT 1 in pulse period PT1and molten droplet 24 d is removed after base current period IBT1, thatis, removal time point td when molten droplet 24 d is removed is late inpeak current period IPT 2 of pulse period PT 2 next to pulse period PT1,it is determined that the melting speed of welding wire 24 is too low.In order to set the area of the optimum pulse waveform which is theappropriate melting speed of the welding wire, based on the relationshipbetween pulse frequency PHz and peak current IP illustrated in FIG. 6,in a case where peak current IP increases from reference value 460 A to500 A, stable arc length L28 can be secured by pulse frequency PHzdecreasing from reference value 210 Hz to 195 Hz.

As described above, based on the predetermined relationship betweenpulse frequency PHz and peak current IP, if removal time point td atwhich molten droplet 24 d is removed is not in base current period IBT1,peak current IP as the pulse waveform parameter is adjusted and pulsefrequency PHz is adjusted such that removal time point td is in basecurrent period IBT1. Specifically, in a case where removal time point tdis earlier than base current period IBT1, that is, before base currentperiod IBT1, welding controller 31 b decreases peak current IP andincreases pulse frequency PHz. In a case where removal time point td islater than base current period IBT1, that is, after base current periodIBT1, peak current IP and pulse frequency PHz, which are pulse waveformparameters, are adjusted so as to increase peak current IP and decreasepulse frequency PHz.

In pulse arc welding device 1001 according to Embodiment 1, by adjustingnot peak current IP but the length of peak current period IPT, thetiming at which molten droplet 24 d is removed can be adjusted. FIG. 7illustrates states of welding voltage V, welding current I, weldingcurrent I a state of the welding transfer in a case where a timing atwhich molten droplet 24 d of the molten droplet transfer (dropletremoval) state is removed by adjusting peak current period IPT isadjusted. With respect to state Sd1 in which molten droplet 24 d isremoved from the tip of welding wire 24 in pulse falling period IPFTbefore base current period IBT in the unstable molten droplet transfer(droplet removal) state illustrated in FIG. 3, as illustrated in FIG. 7,peak current period IPT is shortened to reduce the area of the pulsewaveform, and the electrical energy applied to welding wire 24 isreduced to be appropriate.

In welding current I illustrated in FIG. 7, since the pulse area issmall, in order to secure an appropriate melting speed of welding wire24, peak current period IPT and pulse period PT are shortened toincrease pulse frequency PHz to adjust peak current period IPT and pulsefrequency PHz which are a pulse waveform parameter so that weldingcurrent I becomes the setting current which is an appropriate averagecurrent. This operation provides an optimal state of molten droplettransfer timing in which molten droplet 24 d is removed in base currentperiod IBT while stabilizing arc length L28.

In the above method for adjusting removal time point td at the moltendroplet transfer by adjusting peak current period IPT, conversely, in astate of molten droplet transfer (droplet removal) state illustrated inFIG. 4, in state Sf2, molten droplet 24 d is not removed during basecurrent period IBT1 in pulse period PT1, after base current period IBT1,that is, in peak current period IPT2 in pulse period PT2 next to pulseperiod PT1, molten droplet 24 d becomes an unstable molten droplettransfer (droplet removal) state of being enlarged and removed by thegravity. For state Sf2, peak current period IPT is lengthened, the areaof the pulse waveform in one pulse period PT increases so as to optimizethe electric energy applied to welding wire 24 for securing theappropriate melting speed of welding wire 24.

In welding current I described above, since the area of the pulsewaveform increases, in order to secure the same melting speed, thelengthening of peak current period IPT and the lengthening of pulseperiod PT to lower pulse frequency PHz can adjust the molten droplettransfer (removal) state to be the optimal state while stabilizing arclength L28.

An example of specific adjustment of peak current period IPT and pulsefrequency PHz in pulse arc welding device 1001 will be described below.FIG. 8 illustrates a predetermined relationship between peak currentperiod IPT and pulse frequency PHz, which are pulse waveform parametersfor optimally adjusting the molten droplet transfer (removal) statewhile stabilizing arc length L28.

FIG. 8 illustrates a predetermined relationship between peak currentperiod IPT and pulse frequency PHz, which are pulse waveform parametersin a case where the diameter of welding wire 24 is ϕ1.2 and the settingcurrent of welding current I is 200 A in the pulse MAG welding in whichwelding wire 24 is mild steel. In the relationship illustrated in FIG.8, the reference value of peak current period IPT is 620 μs and thereference value of pulse frequency PHz is 210 Hz.

Adjustment of pulse waveform parameters based on the relationshipillustrated in FIG. 8 of pulse arc welding device 1001 will be describedbelow. In the example shown in FIG. 8, welding wire 24 or shielding gasdifferent from the recommended conditions is used.

As illustrated in FIG. 3, in a case where molten droplet 24 d is removedbefore base current period IBT and the timing of droplet removal is tooearly, it is determined that the melting speed of welding wire 24 is toohigh. In order to obtain the optimum pulse waveform area as the meltingspeed of welding wire 24, based on the predetermined relationshipbetween pulse frequency PHz and peak current period IPT illustrated inFIG. 8, in a case where peak current period IPT is shortened fromreference value 620 μs to 580 μs, stable arc length L28 can be securedby increasing pulse frequency PHz from reference value 210 Hz to 215 Hz.

In contrast, as illustrated in FIG. 4, in pulse period PT1, in a casewhere molten droplet 24 d is not removed during base current period IBT1 and molten droplet 24 d is removed after base current period IBT1,that is, removal period td in which molten droplet 24 d is removed islate to peak current period IPT 2 in pulse period PT 2 next to pulseperiod PT1, it is determined that the melting speed is too small. Inorder to obtain the optimum pulse waveform area which is the appropriatemelting speed of welding wire 24, based on the predeterminedrelationship between pulse frequency PHz and peak current period IPTillustrated in FIG. 8, in a case where peak current period IPT islengthened from the reference value of 620 μs to 700 μs, stable arclength L28 can be secured by decreasing pulse frequency PHz fromreference value 210 Hz to 195 Hz.

As described above, when removal time point td at which molten droplet24 d is removed is not in base current period IBT1, peak current periodIPT as the pulse waveform parameter is adjusted so as to be in basecurrent period IBT1, and pulse frequency PHz is adjusted based on thepredetermined relationship between pulse frequency PHz and peak currentperiod IPT. Specifically, in a case where removal time point td at whichmolten droplet 24 d is removed is too early, peak current period IPTdecreases and pulse frequency PHz increases. In a case where removaltime point td is too late, peak current period IPT increases and pulsefrequency PHz decreases, and thus peak current period IPT and pulsefrequency PHz which are pulse waveform parameters are adjusted.

It is determined that whether or not to change peak current IP and peakcurrent period IPT from the reference value to the optimal numericalvalue by welding voltage V being monitored in real time in monitoring ofthe molten droplet transfer (droplet removal) state, and a state whereconstriction 24 p is produced in base current period IBT being detected.That is, a time differential value obtained by differentiating weldingvoltage V with respect to time is compared to a predetermined value soas to determine removal time point td at which molten droplet 24 d isremoved from welding wire 24. Droplet-removal detector 13 of arccontroller 12 of welding controller 31 b can determine removal timepoint td to be a time point at which droplet-removal detector 13 detectsa predetermined change of the differential value exceeding apredetermined value from below the predetermined value.

In a case where welding controller 31 b detects that the timedifferential value of welding voltage V exceeds a predetermined valuefrom a value smaller than the predetermined value at one or for eachtime of the pulse period with peak current period IPT or pulse fallingperiod IPFT before base current period IBT, welding controller 31 bdetermines that the melting speed of welding wire 24 is high and theelectric energy for melting welding wire 24 is relatively large. Then,welding controller 31 b adjusts the pulse waveform parameter to decreasepeak current IP of the pulse waveform parameter or to decrease peakcurrent period IPT.

In a case of adjusting peak current IP by decreasing peak current IP,welding controller 31 b decreases peak current IP by a predeterminedchange, e.g. by the value of 5 A, for each pulse period PT while peakcurrent IP is adjusted by monitoring the time differential value foreach pulse period PT until the predetermined change of time differentialvalue of welding voltage V in base current period IBT is detected. Whenthe predetermined change of the time differential value of weldingvoltage V in base current period IBT is detected in one or each pulseperiod PT, the decrease of peak current IP is stopped.

Even in a case where peak current period IPT is reduced to be adjusted,similarly, while welding controller 31 b decreases peak current periodIPT by a predetermined change, e.g. by a value of 10 μs, for each pulseperiod PT, if welding controller 31 b detects the predetermined changein welding voltage V in base current period IBT in one or each pulseperiod PT, welding controller 31 b stops the decreasing of peak currentperiod IPT.

In contrast, in a case where welding controller 31 b detects the changeof the time differential value of welding voltage V after base currentperiod IBT of pulse period PT1, specifically at the time point afterpulse period PT2 next to pulse period PT1 or in a case where weldingcontroller 31 b detects the predetermined change of the timedifferential value at a rate of one time in plural pulse periods PTwithout detecting the predetermined change of welding voltage V for eachpulse period PT, welding controller 31 b determines that the weldingspeed of welding wire 24 is late and the electric energy for meltingwelding wire 24 is relatively small. Then, welding controller 31 badjusts the pulse waveform parameter so as to increase peak current IPor increase peak current period IPT as the pulse waveform parameter.

In a case of adjusting by increasing peak current IP, since weldingcontroller 31 b increases peak current IP by a predetermined change,e.g. a value of 5 A for each pulse period PT, welding controller 31 badjusts peak current IP by monitoring the time differential value ofwelding voltage V for each pulse period PT until the predeterminedchange of the time differential value of welding voltage V in basecurrent period IBT is detected. When welding controller 31 b detects thepredetermined change of the time differential value of welding voltage Vin base current period IBT in one or each pulse period, weldingcontroller 31 b stops the increase of peak current IP.

In addition, similarly, even in a case of being adjusted and increasingpeak current period IPT, since welding controller 31 b increases peakcurrent period IPT by a predetermined change, e.g. a value of 10 μs foreach pulse period PT, when detecting the predetermined change of thetime differential value of welding voltage V in one or each pulse periodPT, welding controller 31 b stops the increase of peak current periodIPT.

Droplet-removal detector 13 may determine removal time point td at whichmolten droplet 24 d is removed from by the value of welding voltage Vinstead of the time differential value of welding voltage V.

Removal time point td at which molten droplet 24 d is removed fromwelding wire 24 may be determined by the resistance value obtained bydividing welding voltage V by welding current I. In this case, forexample, droplet-removal detector 13 determines removal time point td tobe a time point at which a predetermined change in which the timedifferential value obtained by differentiating the resistance value withrespect to time exceeds the predetermined value from below thepredetermined value is detected. Droplet-removal detector 13 maydetermine removal time point td with the resistance value itself insteadof the time differential value of the resistance value. In a case wherethe change of welding voltage V caused by the removal of molten droplet24 d is small, since removal time point td may be erroneously determinedbased on welding voltage V, it is preferable to determine removal timepoint td.

In a case where the molten droplet transfer (droplet removal) state ismonitored and the molten droplet transfer timing in the molten droplettransfer (droplet removal) state is performed by adjusting the pulsewaveform parameter, it is also possible to combine adjustment of aplurality of parameters of each pulse waveform parameter. In theoperation described above, peak current IP and peak current period IPTare adjusted to adjust removal time point td at which molten droplet 24d is removed. In pulse arc welding device 1001, welding controller 31 bcan adjust removal time point td by adjusting both peak current IP andpeak current period IPT. In this case, in a case where both peak currentIP and peak current period IPT are adjusted together based on thepredetermined relationship with pulse frequency PHz illustrated in FIGS.6 and 8, correlated pulse frequency PHz is also adjusted at the sametime. By using plural parameters instead of one of the pulse waveformparameters, since the amount of change per one parameter can be reduced,the adjustment range of removal time point td can be widened.

Specifically, in pulse arc welding device 1001 according to Embodiment1, both peak current IP and peak current period IPT of welding current Iare adjusted and pulse frequency PHz is adjusted as follows.

For example, in a case where removal time point td is advanced whileremoval time point td of molten droplet 24 d is too late as illustratedin FIG. 4, welding controller 31 b increases peak current IP. In a casewhere peak current IP exceeding the maximum value that can be output bywelding power supply unit 31 a is required to cause removal time pointtd to be in base current period IBT as illustrated in FIG. 2, weldingcontroller 31 b increase peak current period IPT after increasing peakcurrent IP to near the maximum value. Welding controller 31 b increasespeak current IP and adjusts pulse frequency PHz based on thepredetermined relationship between peak current IP and pulse frequencyPHz illustrated in FIG. 6, and increases peak current period IPT andadjusts pulse frequency PHz based on the predetermined relationshipbetween peak current period IPT and pulse frequency PHz illustrated inFIG. 8.

Alternatively, welding controller 31 b increases peak current period IPTin a case of advancing removal time point td of the removal of moltendroplet 24 d. In addition, as illustrated in FIG. 2, when peak currentperiod IPT increases to cause removal time point td to be in basecurrent period IBT, peak current period IPT1 in pulse period PT1 is tooclose to peak current period IPT2 in next pulse period PT2, so that basecurrent period IBT1 becomes short and the pulse waveform cannot beformed. In this case, welding controller 31 b increases peak currentperiod IPT after increasing peak current period IP to near maximumallowable value thereof and then increases peak current IP. Weldingcontroller 31 b increases peak current period IPT and adjusts pulsefrequency PHz based on the predetermined relationship between peakcurrent period IPT and pulse frequency PHz illustrated in FIG. 8, andincreases peak current IP and adjusts pulse frequency PHz based on thepredetermined relationship between peak current IP and pulse frequencyPHz illustrated in FIG. 6.

The material of welding wire 24 allowing a waveform illustrating a statewhere constriction 24 p is produced by welding voltage V to likelyappear is a soft steel wire or an aluminum wire. For the stainless steelwire, since a waveform illustrating a state where constriction 24 p isproduced by welding voltage V is unlikely to appear, it is difficult todetect the occurrence of constriction 24 p.

In the pulse arc welding control method in Embodiment 1, pulse weldingis performed in which an arc is generated between welding wire 24 andobject 29, and peak current period IPT and base current period IBT arerepeated. The time differential value of welding voltage V duringwelding is monitored. In a case where the time differential valueexceeds a predetermined value, it is determined that molten droplet 24 dis removed. If removal time point td at which molten droplet 24 d isremoved is not in base current period IBT, peak current IP and/or peakcurrent period IPT of the pulse waveform parameter are adjusted andpulse frequency PHz is adjusted based on the predetermined relationshipbetween pulse frequency PHz and peak current IP to cause removal timepoint td to be in base current period IBT.

In welding power supply device 31 illustrated in FIG. 1,short-circuit/arc detector 10 determines whether a short-circuit or anarc is generated between welding wire 24 and object 29 based on theoutput of welding voltage detector 8 and/or the output of weldingcurrent detector 9. Short-circuit controller 11 controls outputcontroller 7 during the short-circuit period in which a short-circuitoccurs. Arc controller 12 controls output controller 7 during the arcperiod in which an arc is generated.

Pulse waveform setting unit 14 sets the pulse waveform during the arcperiod.

In welding power supply device 31, upon receiving a signal indicatingthat a short-circuit is generated from short-circuit/arc detector 10,short-circuit controller 11 controls circuit current IS flowing inwelding wire 24 during the short-circuit period to open theshort-circuit.

Upon receiving from short-circuit/arc detector 10 a signal indicatingthat an arc is generated, arc controller 12 causes pulse waveformsetting unit 14 of arc controller 12 to send the pulse waveformparameter, such as peak current IP, base current IB, peak current periodIPT, and base current period IBT to pulse waveform controller 15.

In the arc state, droplet-removal detector 13 of arc controller 12monitors welding voltage V detected by welding voltage detector 8 inreal time to detect removal time point td at which the time differentialvalue of the welding voltage V exceeds a predetermined value indicatingthat molten droplet 24 d is removed. Arc controller 12 determineswhether or not removal time point td is in base current period IBT.

If removal time point td at which molten droplet 24 d is removed is inbase current period IBT, arc controller 12 continues outputting thepulse waveform parameter output from pulse waveform setting unit 14 asit is. If removal time point td is out of base current period IBT, thepulse waveform parameter which is at least one of peak current IP andpeak current period IPT is adjusted and corresponding to this, pulsefrequency PHz based on the predetermined relationship between pulsewaveform parameter and pulse frequency PHz is adjusted. Accordingly,while gradually changing the pulse waveform parameter, which is at leastone of peak current IP and peak current period IPT, so that moltendroplet 24 d is removed in base current period IBT, removal time pointtd is adjusted as described above. Contents of the adjustment are storedin peak current corrector 16, peak current period corrector 17, andpulse frequency corrector 18, which correspond respectively in pulsewaveform controller 15.

The relationship illustrated in FIGS. 6 and 8 can be experimentallyobtained as follows. For each of samples of the welding wire 24 made ofvarious materials and having various diameters, for example, peakcurrent IP which is a pulse waveform parameter is adjusted, and pulsefrequency PHz is adjusted correspondingly to cause molten droplet 24 dto be removed in base current period IBT and perform the molten droplettransfer. Based on this adjustment, peak current IP of the correspondingpulse waveform parameter and the value of pulse frequency PHz are storedin a database of respective correctors, such as peak current corrector16, peak current period corrector 17, and pulse frequency corrector 18,thereby obtaining the relation between peak current IP and pulsefrequency PHz illustrated in FIG. 6. Similarly, for each of samples ofthe welding wire 24 made of various materials of welding wire 24 andhaving various diameters, peak current period IPT which is a pulsewaveform parameter is adjusted to remove molten droplet 24 d in basecurrent period IBT and perform the molten droplet transfer, and pulsefrequency PHz is adjusted accordingly. Based on this adjustment, thevalues of peak current period IPT and pulse frequency PHz of thecorresponding pulse waveform parameters are stored in the database ofthe respective correctors, such as peak current corrector 16, peakcurrent period corrector 17, and pulse frequency corrector 18, and therelation between peak current period IPT and pulse frequency PHzillustrated in FIG. 8 is obtained.

For example, in the setting of the setting current as the movingaverage, peak current IP which is a pulse waveform parameter is adjustedfor the setting current values changing by 20 A in the range of thesetting current from 100 A to 300 A, and pulse frequency PHz is adjustedcorrespondingly such that molten droplet 24 d is removed to perform themolten droplet transfer in base current period IBT. Based on thisadjustment, peak current IP of the corresponding pulse waveformparameter and the value of pulse frequency PHz are stored in thedatabase of respective correctors, such as peak current corrector 16,peak current period corrector 17, and pulse frequency corrector 18,thereby obtaining the relation between peak current IP and pulsefrequency PHz illustrated in FIG. 6. Similarly, peak current period IPTwhich is a pulse waveform parameter is adjusted and pulse frequency PHzis adjusted correspondingly such that molten droplet 24 d is removed inbase current period IBT to perform molten droplet transfer with respectto values of the setting current changing by 20 A in the range from 100A to 300 A and perform molten droplet transfer. Based on thisadjustment, the values of peak current period IPT and pulse frequencyPHz of the corresponding pulse waveform parameters are stored in thedatabase of the respective correctors such as peak current corrector 16,peak current period corrector 17, and pulse frequency corrector 18,thereby obtaining the relation between peak current period IPT and pulsefrequency PHz illustrated in FIG. 8. These operations provide stablewelding in a wide range of welding current I.

In addition, for example, at the value of the feeding speed of weldingwire 24 for each 1 m/min in a range from 1 m/min to 10 m/min such thatmolten droplet 24 d is removed in base current period IBT to perform themolten droplet transfer, peak current IP which is a pulse waveformparameter is adjusted, and pulse frequency PHz is adjustedcorrespondingly. On the basis of this adjustment, the values of peakcurrent IP and pulse frequency PHz of the corresponding pulse waveformparameter are stored in the database of respective correctors, such aspeak current corrector 16, peak current period corrector 17, and pulsefrequency corrector 18, thereby obtaining the relation between peakcurrent IP and pulse frequency PHz illustrated in FIG. 6. Similarly,peak current period IPT which is a pulse waveform parameter is adjusted,and pulse frequency PHz is adjusted correspondingly such that moltendroplet 24 d is removed in base current period IBT to perform the moltendroplet transfer with respect to the values of the feeding speed ofwelding wire 24 changing by 1 m/min in the range from 1 m/min to 10m/min. Based on this adjustment, the values of peak current IP and pulsefrequency PHz of the corresponding pulse waveform parameter are storedin the database of respective correctors, such as peak current corrector16, peak current period corrector 17, and pulse frequency corrector 18,thereby obtaining the relation between peak current period IPT and pulsefrequency PHz illustrated in FIG. 8. This operation provides stablewelding in a wide range of the welding speed of welding wire 24.

In addition to having the values of peak current IP, peak current periodIPT, and pulse frequency PHz illustrating the relationship illustratedin FIGS. 6 and 8 as a database, it may be stored as a function, such asa linear function or a quadratic function, that approximates thesevalues by interpolating.

It is possible to smoothly set the welding condition with the value ofthe pulse waveform parameter for adjusting the timing of molten droplettransfer (droplet removal) by deriving the value of the pulse waveformparameter by welding the test piece in a step before the weldingcondition is given.

In the case that the welding wire used by the user has differentviscosity, surface tension and the like than the welding wirerecommended by the welding machine manufacturer, the state of moltendroplet transfer may greatly change, there is also no regularity at thetiming of molten droplet transfer (droplet removal). This may notprovide stable welding.

In a case where removal time point td at which molten droplet 24 d isremoved is in base current period IBT, welding controller 31 b sets apulse waveform parameter which is at least one of peak current IP andpeak current period IPT, and pulse frequency PHz such that removal timepoint td is in predetermined base current period IBT. In a case whereremoval time point td at which molten droplet 24 d is removed is in basecurrent period IBT, welding controller 31 b maintains the pulse waveformparameter and pulse frequency PHz so that removal time point td is inbase current period IBT.

A pulse arc welding machine can ordinarily perform one welding transfer(droplet removal) per one peak current synchronously with the peakcurrent, by selecting appropriate welding condition set separately forthe welding wire recommended by the welding machine manufacturer.

However, in a case where it is difficult to appropriately perform moltendroplet transfer (droplet removal) during the peak current period bychanging the welding wire or welding conditions, a molten droplet may beremoved at a rate of one for several time of peak currents, which makesthe droplet transfer (droplet removal) unstable. In addition, largemolten metal cumulatively adheres to the tip of the welding wire, isshort-circuited with the base material, and causes spattering.

FIG. 9 illustrates the welding current in the pulse arc welding of thecomparative example for solving the problem described above. In thispulse arc welding method, in order to improve the stability of moltendroplet transfer (droplet removal) to improve welding workability, asillustrated in FIG. 9, until the molten droplet transfer (removal)occurs, peak current period TP continues and droplet transfer (removal)is reliably generated one time per one period of the pulse.

However, although the one drop per one pulse is surely performed, whiletime point td at which molten droplet transfer (droplet removal) isperformed is in peak current period TP, the length of peak currentperiod TP is changed for each time. Therefore, since the pulseperiodicity varies, the arc length fluctuates largely and may losewelding stability, hence causing instability of welding to appear on theouter appearance of the bead.

In the event that a short-circuit occurs with a base material beforemolten droplet transfer (droplet removal), a large amount of spatteringmay be produced with a short-circuit at a high peak current value.Therefore, in this pulse arc welding, welding stability may not besecured.

In the pulse arc welding control method and pulse arc welding device1001 in accordance with Embodiment 1, a molten droplet transfer (dropletremoval) state is detected. If removal time point td of the moltendroplet transfer (droplet removal) is not in base current period IBT,peak current IP and/or peak current period IPT as the pulse waveformparameter is adjusted, and pulse frequency PHz is adjusted such that thepulse waveform is within base current period IBT, thereby performingstable welding of one drop per one pulse of one pulse period PT, andproviding high welding quality, such as obtaining a homogeneous bead.

Exemplary Embodiment 2

FIG. 10 is a schematic diagram of pulse arc welding device 1002according to Exemplary Embodiment 2. In FIG. 10, components identical tothose of pulse arc welding device 1001 according to Embodiment 1illustrated in FIG. 1 are denoted by the reference numerals. Pulse arcwelding device 1002 according to Embodiment 2 does not includedroplet-removal detector 13 of welding controller 31 b of pulse arcwelding device 1001 according to Embodiment 1.

In pulse arc welding device 1002, short-circuit/arc detector 10 detectsa short-circuit between welding wire 24 and object 29 based on weldingvoltage V, thereby detecting that the molten droplet is removed fromwelding wire 24. In order to eliminate unstable molten droplet transferstate due to different welding conditions, such as welding wire 24 andshielding gas to be used, pulse arc welding device 1002 is designed suchthat molten droplet transfer state becomes an optimal state. If removaltime point td of molten droplet transfer (droplet removal) is not inbase current period IBT, one or more pulse waveform parameters areadjusted such that removal time point td is in base current period IBT,and the one or more pulse waveform parameters are adjusted such that thetime point described above is in base current period IBT.

FIG. 11 illustrates welding current I, welding voltage V, and a state ofmolten droplet transfer when welding controller 31 b adjusts the removaltime point at which molten droplet 24 d of the molten droplet transferis removed from welding wire 24 at peak current IP in pulse arc weldingdevice 1002 in accordance with Embodiment 2. In FIG. 11, items identicalto welding current I, welding current I, and a state of molten droplettransfer in pulse arc welding device 1001 according to Embodiment 1illustrated in FIG. 1 will be denoted by the same reference numerals.Specifically, before adjustment of the pulse waveform parameter, whichis at least one of peak current IP and peak current period IPT,short-circuit/arc detector 10 detects a short-circuit between weldingwire 24 and object 29 during actual welding in real time. Weldingcontroller 31 b determines that the electric energy for melting weldingwire 24 is excessive, in a state (broken line state Sc11 of weldingvoltage V) where molten droplet 24 d is short-circuited with object 29at the tip of welding wire 24 in pulse falling period IPFT before basecurrent period IBT earlier than base current period IBT. In this case,welding controller 31 b decreases peak current IP, which is a pulsewaveform parameter, reduces the area of the pulse waveform, andoptimizes electrical energy so as to obtain welding current I andwelding voltage V illustrated by the solid line in FIG. 11. When weldingwire 24 is short-circuited with object 29 via molten droplet 24 d,welding power supply unit 31 a causes short-circuit current IS to flowthrough welding wire 24.

In the waveform parameters illustrated in FIG. 11, since the area of thepulse waveform is small, pulse period PT is shortened and pulsefrequency PHz is adjusted to be high in order to secure an appropriatewire melting speed. Accordingly, peak current IP and pulse frequency PHzwhich are pulse waveform parameters are adjusted such that the averagevalue of welding current I becomes the appropriate setting current.Removal time point td at which molten droplet 24 d is removed fromwelding wire 24 while arc length L28 is stabilized can be adjusted tothe timing of the optimal state in base current period IBT.

Before adjustment of the pulse waveform parameter, a short-circuitduring welding is detected in real time, molten droplet 24 d is notremoved during base current period IBT, molten droplet 24 d is enlargedat peak current period IPT after base current period IBT later than basecurrent period IBT, and then, welding wire 24 is short-circuited withobject 29 via molten droplet 24 d contacting object 29 at the tip ofwelding wire 24. In this case, welding controller 31 b determines thatthe melting speed of welding wire 24 is excessively small and thus theelectric energy for melting welding wire 24 is excessively small. Then,welding controller 31 b increases peak current IP, which is a pulsewaveform parameter, to increase the area of the pulse waveform to makethe electrical energy appropriate.

In the control described above, since the area of the pulse waveformincreases, in order to secure the appropriate melting speed of weldingwire 24 properly, welding controller 31 b simultaneously increases pulseperiod PT and adjusts pulse frequency PHz to be low. As described above,welding controller 31 b adjusts peak current IP and pulse frequency PHz,which are pulse waveform parameters, so that the average value ofwelding current I becomes properly setting current. Welding controller31 b thus adjusts removal time point td at which molten droplet 24 d isremoved to an optimal state which is in base current period IBT whilemaking stable arc length L28.

FIG. 12 illustrates welding current I and welding voltage V and a stateof short-circuit transfer when the short-circuit transfer timing atwhich molten droplet 24 d is short-circuited with object 29 in peakcurrent period IPT is adjusted by detecting the short-circuit duringwelding in real time. Specifically, short-circuit/arc detector 10detects molten droplet transfer (short-circuit), molten droplet 24 d isremoved from welding wire 24 before base current period IBT. For a state(state Sf12 at welding current I and welding voltage V indicated bybroken line) where molten droplet 24 d is short-circuited with object 29at the tip of welding wire 24 in pulse falling period IPFT, weldingcontroller 31 b shortens peak current period IPT which is a pulsewaveform parameter to reduce the area of the pulse waveform to make theelectric energy appropriate so as to obtain welding current I andwelding voltage V indicated by the solid line.

In the control illustrated in FIG. 12, since the area of the pulsewaveform is small, in order to secure the appropriate melting speed ofwelding wire 24, welding controller 31 b can adjust the timing of theoptimal state where removal time point td of the molten droplet transfer(short-circuit) is in base current period IBT while stabilizing arclength L28 by shortening pulse period PT to increase pulse frequencyPHz.

A short-circuit during welding is detected in real time, a short-circuitdoes not occur during base current period IBT1 of pulse period PT1,molten droplet 24 d is enlarged in peak current period IPT2 of nextpulse period PT 2 after base current period IBT1, and molten droplet 24d is short-circuited with object 29 at the tip of welding wire 24. Inthis case, it is in an unstable molten droplet transfer (short-circuit)state. In this case, peak current period IPT, which is a pulse waveformparameter, is lengthened, the area of the pulse waveform is increased,and the electrical energy becomes appropriate in order to secure anappropriate melting speed of welding wire 24.

In the adjustment described above of the pulse waveform parameter, sincethe area of the pulse waveform increases, in order to secure the meltingspeed of welding wire 24 identical to the melting speed of welding wire24 before the area is increased, welding controller 31 b simultaneouslyincreases pulse period PT, decreases pulse frequency PHz and thus peakcurrent period IPT and pulse frequency PHz which are the pulse waveformparameters are adjusted such that the average value of welding current Ibecomes the setting current. Accordingly, removal time point td at whichthe short-circuit is generated and molten droplet 24 d is removed whilearc length L28 is stabilized is adjusted to be the timing of the optimalstate that becomes base current period IBT so that short-circuit occursduring base current period IBT1.

Similarly to pulse arc welding device 1001 in Embodiment 1, pulse arcwelding device 1002 may adjust the time point at which molten droplet 24d is short-circuited with object 29, that is, removal time point td byadjusting both peak current IP and peak current period IPT and adjustingpulse frequency PHz.

In pulse arc welding device 1002 according to Embodiment 2, an arc isgenerated between welding wire 24 and object 29 to perform pulse weldingrepeating peak current period IPT and base current period IBT.Short-circuit/arc detector 10 of welding controller 31 b detects ashort-circuit during welding, and determines the time point when theshort-circuit is detected, that is, the time point when the time pointis detected based on the short-circuit, as removal time point td atwhich molten droplet 24 d is removed. Welding controller 31 b adjusts atleast one of peak current IP and peak current period IPT so that thetime point when the short-circuit is detected is in base current periodIBT, and adjusts pulse frequency PHz based on at least one of thepredetermined relationship between pulse frequency PHz and peak currentIP illustrated in FIG. 6 of pulse arc welding device 1001 in accordancewith Embodiment 1 and the predetermined relationship between pulsefrequency PHz and peak current period IPT illustrated in FIG. 8.

Compared to recommended welding conditions, such as welding wire andshielding gas recommended by welding machine manufacturers, if thewelding wire used by the user has different welding conditions, such asviscosity, surface tension, and shielding gas, the molten droplettransfer form greatly differs, and thus there is also no regularity inthe timing of molten droplet transfer timing, and therefore, stablewelding may not be performed.

In the pulse arc welding method and pulse arc welding device 1002 inaccordance with Embodiment 2, a short-circuit of molten droplet 24 d isdetected. If removal time point td at which molten droplet 24 d isremoved is not in base current period IBT, the pulse waveform parameterwhich is at least one of peak current IP and peak current period IPT isadjusted and pulse frequency PHz is adjusted such that removal timepoint td is in base current period IBT. This operation provides stablemolten droplet transfer (droplet removal), stable pulse welding, andhomogeneous welding quality.

As described above, the pulse arc welding control method uses a pulsearc welding device 1001 (1002) that welds an object 29 by generating anarc between a welding wire 24 and the object 29. Pulse arc weldingdevice 1001 (1002) is controlled so as to weld the object 29 byremoving, from the welding wire 24, a molten droplet 24 d produced bymelting the welding wire 24 by applying a welding voltage V between thewelding wire 24 and the object 29 and allowing a welding current I toflow through the welding wire 24 such that the welding current Ialternately repeats, at pulse frequency PHz, a peak current period IPTin which the welding current I is a peak current IP and a base currentperiod IBT in which the welding current I is a base current IB smallerthan the peak current IP. Removal time point td at which the moltendroplet 24 d is removed from the welding wire 24 is determined. In acase where the removal time point td is not in the base current periodIBT, a pulse waveform parameter which is at least one of the peakcurrent IP and the peak current period IPT is adjusted. Pulse frequencyPHz is adjusted based on a predetermined relationship between the pulsefrequency PHz and the pulse waveform parameter so as to cause theremoval time point td to be in the base current period IBT.

In a case where removal time point td is before base current period IBT,peak current IP may be decreased and pulse frequency PHz may beincreased. In a case where removal time point td is after base currentperiod IBT, peak current IP may be increased and pulse frequency PHz maybe decreased.

In a case where removal time point td is before base current period IBT,peak current period IPT may be decreased and pulse frequency PHz may beincreased. In a case where removal time point td is after peak currentperiod IPT, peak current period IPT may be increased and pulse frequencyPHz may be decreased.

Pulse arc welding device 1001 (1002) may be controlled such that weldingcurrent I alternately repeats peak current period IPT and base currentperiod IBT at pulse frequency PHz over plural pulse periods PT. In thiscase, the pulse waveform parameter is gradually adjusted over pulseperiods PT and pulse frequency PHz is gradually adjusted over pulseperiods PT. When removal time point td enters base current period IBT,the adjustment of the pulse waveform parameter is terminated andadjustment of pulse frequency PHz is terminated.

The pulse waveform parameter may be peak current IP. The pulse waveformparameter may be peak current period IPT. The pulse waveform parametermay be peak current IP and peak current period IPT.

A time point when the time differential value obtained bydifferentiating welding voltage V with time exceeds a predeterminedvalue from below the predetermined value may be determined as removaltime point td.

A time point at which the time differential value obtained bydifferentiating the resistance value obtained by dividing weldingvoltage V by welding current I with time exceeds a predetermined valuefrom below the predetermined value may be determined as removal timepoint td.

The removal time point td at which molten droplet 24 d is removed fromwelding wire 24 may be determined based on the time point at which theshort-circuit between welding wire 24 and object 29 is detected.

The pulse waveform parameter and pulse frequency PHz may be set suchthat removal time point td is in base current period IBT in a case whereremoval time point td is in base current period IBT. In this case, thepulse waveform parameter and pulse frequency PHz may be maintained.

In pulse arc welding device 1001 (1002), an arc is generated betweenwelding wire 24 and object 29 to weld object 29. Pulse arc weldingdevice 1001 (1002) includes wire feeder 25 that feeds welding wire 24,welding power supply unit 31 a that outputs welding voltage V andwelding current I, welding controller 31 b that controls welding powersupply unit 31 a. Welding controller 31 b is configured to control thewelding power supply unit 31 a so as to weld the object 29 by removing,from the welding wire 24, a molten droplet 24 d produced by melting thewelding wire 24 by applying a welding voltage V between the welding wire24 and the object 29 and allowing a welding current I to flow throughthe welding wire 24 such that the welding current I alternately repeats,at pulse frequency PHz, a peak current period IPT in which the weldingcurrent I is a peak current IP and a base current period IBT in whichthe welding current I is a base current IB smaller than the peak currentIP. Welding controller 31 b is configured to determine a removal timepoint td at which the molten droplet 24 d is removed from the weldingwire 24. In a case where the removal time point td is not in the basecurrent period IBT, welding controller 31 b is configured to adjust apulse waveform parameter which is at least one of the peak current IPand the peak current period IPT and adjust the pulse frequency PHz basedon a predetermined relationship between the pulse frequency PHz and thepulse waveform parameter so as to cause the removal time point td is inthe base current period IBT.

Welding controller 31 b includes welding condition setting unit 21 forsetting a setting current which is a value of welding current I, feedingspeed controller 19 that controls the feeding speed at which wire feeder25 feeds the wire based on the setting current, and pulse waveformsetting unit 14 that outputs a signal corresponding to the waveform ofwelding current I based on the setting current or the wire feedingspeed.

The arc welding control method in accordance with Embodiments 1 and 2provide stable pulse welding even in a case where the user does not usewelding conditions, such as welding wire and shielding gas, recommendedby the welding machine manufacturer. These arc welding control methodsare useful for a welding device that performs arc welding whilecontinuously feeding a welding wire that is a consumable electrode.

REFERENCE MARKS IN THE DRAWINGS

-   IP peak current-   IPT, IPT1, IPT2, TP peak current period-   IB base current-   IBT, IBT1, IBT2 base current period-   IPRT, IPRT1, IPRT2 pulse rising period-   IPFT, IPFT1, IPFT2 pulse falling period-   PHz pulse frequency-   PT, PT1, PT2 pulse period-   1 input power supply-   2 primary rectifier-   3 switching element-   4 transformer-   5 secondary rectifier-   6 reactor-   7 output controller-   8 welding voltage detector-   9 welding current detector-   10 short-circuit/arc detector-   11 short-circuit controller-   12 arc controller-   13 droplet-removal detector-   14 pulse waveform setting unit-   15 pulse waveform controller-   16 peak current corrector-   17 peak current period corrector-   18 pulse frequency corrector-   19 feeding speed controller-   20 robot controller-   21 welding condition setting unit-   22 robot-   23 welding wire storage unit-   24 welding wire-   25 wire feeder-   26 torch-   27 chip-   28 arc-   29 object-   30 a output terminal-   30 b output terminal-   31 welding power supply device-   31 a welding power supply unit-   31 b welding controller-   1001 pulse arc welding device-   1002 pulse arc welding device

1. A pulse arc welding control method using a pulse arc welding devicethat welds an object by generating an arc between a welding wire and theobject, the method comprising: controlling the pulse arc welding deviceso as to weld the object by removing, from the welding wire, a moltendroplet produced by melting the welding wire by applying a weldingvoltage between the welding wire and the object and allowing a weldingcurrent to flow through the welding wire such that the welding currentalternately repeats, at pulse frequency, a peak current period in whichthe welding current is a peak current and a base current period in whichthe welding current is a base current smaller than the peak current;determining a removal time point at which the molten droplet is removedfrom the welding wire; and in a case where the removal time point is notin the base current period, adjusting a pulse waveform parameter whichis at least one of the peak current and the peak current period andadjusting the pulse frequency based on a predetermined relationshipbetween the pulse frequency and the pulse waveform parameter so as tocause the removal time point to be in the base current period.
 2. Thepulse arc welding control method according to claim 1, wherein saidadjusting the pulse waveform parameter and adjusting the pulse frequencycomprises: decreasing the peak current and increasing the pulsefrequency in a case where the removal time point is before the basecurrent period; and increasing the peak current and decreasing the pulsefrequency in a case where the removal time point is after the basecurrent period.
 3. The pulse arc welding control method according toclaim 1, wherein said adjusting the pulse waveform parameter andadjusting the pulse frequency comprises: decreasing the peak currentperiod and increasing the pulse frequency in a case where the removaltime point is before the base current period; and increasing the peakcurrent period and decreasing the pulse frequency in a case where theremoval time point is after the peak current period.
 4. The pulse arcwelding control method according to claim 1, wherein said controllingthe pulse arc welding device comprises controlling the pulse arc weldingdevice such that the welding current alternately repeats the peakcurrent period and the base current period at the pulse frequency in aplurality of pulse periods, wherein said adjusting the pulse waveformparameter and adjusting the pulse frequency comprises: graduallyadjusting the pulse waveform parameter and the pulse frequency over theplurality of pulse periods; and terminating the adjusting of the pulsewaveform parameter and the adjusting of the pulse frequency when theremoval time point enters in the base current period.
 5. The pulse arcwelding control method according to claim 1, wherein the pulse waveformparameter is the peak current.
 6. The pulse arc welding control methodaccording to claim 1, wherein the pulse waveform parameter is the peakcurrent period.
 7. The pulse arc welding control method according toclaim 1, wherein the pulse waveform parameter is the peak current andthe peak current period.
 8. The pulse arc welding control methodaccording to claim 1, wherein said determining the removal time pointcomprises determining the removal time point to be a time point at whicha time differential value obtained by differentiating the weldingvoltage with time exceeds a predetermined value from below thepredetermined value.
 9. The pulse arc welding control method accordingto claim 1, wherein said determining the removal time point comprisesdetermining the removal time point to be a time point at which a timedifferential value obtained by differentiating a resistance valueobtained by dividing the welding voltage by the welding current withtime exceeds a predetermined value from below the predetermined value.10. The pulse arc welding control method according to claim 1, whereinsaid determining the removal time point comprises determining theremoval time point based on a time point at which a short-circuitbetween the welding wire and the object is detected.
 11. The pulse arcwelding control method according to claim 1, further comprising in acase where the removal time point is in the base current period, settingthe pulse waveform parameter and the pulse frequency such that theremoval time point is in the base current period.
 12. The pulse arcwelding control method according to claim 11, wherein said setting thepulse waveform parameter and the pulse frequency such that the removaltime point is in the base current period in the case where the removaltime point is in the base current period comprises maintaining the pulsewaveform parameter and the pulse frequency in the case where the removaltime point is in the base current period.
 13. A pulse arc welding devicethat welds an object by producing an arc between a welding wire and theobject, the pulse arc welding device comprising: a wire feeder thatfeeds the welding wire; a welding power supply unit that outputs awelding voltage and a welding current; and a welding controller thatcontrols the welding power supply unit, wherein the welding controlleris configured to: control the welding power supply unit so as to weldthe object by removing, from the welding wire, a molten droplet producedby melting the welding wire by applying a welding voltage between thewelding wire and the object and allowing a welding current to flowthrough the welding wire such that the welding current alternatelyrepeats, at pulse frequency, a peak current period in which the weldingcurrent is a peak current and a base current period in which the weldingcurrent is a base current smaller than the peak current; determine aremoval time point at which the molten droplet is removed from thewelding wire; and in a case where the removal time point is not in thebase current period, adjust a pulse waveform parameter which is at leastone of the peak current and the peak current period and adjust the pulsefrequency based on a predetermined relationship between the pulsefrequency and the pulse waveform parameter so as to cause the removaltime point is in the base current period.
 14. The pulse arc weldingdevice according to claim 13, wherein the welding controller includes awelding condition setting unit for setting a setting current which is avalue of the welding current, a feeding speed controller that controls afeeding speed at which the wire feeder feeds the wire based on thesetting current, and a pulse waveform setting unit that outputs a signalcorresponding to a waveform of the welding current based on the settingcurrent or the wire feeding speed.
 15. The pulse arc welding deviceaccording to claim 13, wherein the pulse waveform parameter is the peakcurrent.
 16. The pulse arc welding device according to claim 13, whereinthe pulse waveform parameter is the peak current period.
 17. The pulsearc welding device according to claim 13, wherein the pulse waveformparameter is the peak current and the peak current period.
 18. The pulsearc welding device according to claim 13, wherein the welding controlleris configured to determine a time point at which a time differentialvalue obtained by differentiating the welding voltage with time exceedsa predetermined value from a value smaller than the predetermined valueas the removal time point.
 19. The pulse arc welding device according toclaim 13, wherein the welding controller is configured to determine theremoval time point to be a time point at which a time differential valueobtained by differentiating a resistance value obtained by dividing thewelding voltage by the welding current with time exceeds a predeterminedvalue from below the predetermined value.
 20. The pulse arc weldingdevice according to claim 13, wherein the welding controller isconfigured to determine the removal time point based on a time point atwhich a short-circuit between the welding wire and the object isdetected.
 21. The pulse arc welding device according to claim 13,wherein the welding controller is configured to, in a case where theremoval time point is in the base current period, set the pulse waveformparameter and the pulse frequency such that the removal time point is inthe base current period.
 22. The pulse arc welding device according toclaim 21, wherein the welding controller is configured to maintain thepulse waveform parameter and the pulse frequency in the case where theremoval time point is in the base current period.